Alzheimer's disease is associated with the abnormal deposits of amyloid beta protein (Ab) which occurs as fibrils within the cerebral neuropil. To characterize the way in which these fibrils assemble we have performed in vitro structural studies on synthetic peptides including the full-length Ab(1-40) as well as Ab(10-35) and Ab(16-22) which all contain the motif KLVFFAE associated with beta-sheet formation. We have used negative-stain transmission electron microscopy to show the presence of fibril formation in these samples which are then analyzed by solid state NMR to determine higher resolution structural information about the organization of the beta-sheets. We have also used scanning transmission electron microscopy (STEM) to map the mass-per-length of the fibrils to obtain information about the numbers of beta-sheets within fibrils formed under different pH conditions. Our results demonstrate how the structure of fibrils grown from Alzheimer-related Ab peptides depends on the peptide length and on the growth conditions.